An unmanned aerial vehicle impact test device

Abstract

The application discloses a kind of simulation unmanned aerial vehicle impact test device, including gas drive unit for output punch, hydraulic energy storage unit is coupled with the punch, and the kinetic energy of punch is converted into controllable hydraulic potential energy and is temporarily stored;Firing unit includes control valve and launch rod, and the control valve is controlled to release the hydraulic potential energy, and launch rod is accelerated;Collision body unmanned aerial vehicle model is driven after being moved and impacts collision body and carries out impact test by the launch rod;Reset unit is used to return the launch rod after firing and make hydraulic oil backflow, realize continuous test.

Description

TECHNICAL FIELD

[0001] The present application relates to a kind of simulation unmanned aerial vehicle impact test device, belong to unmanned aerial vehicle collision simulation field. BACKGROUND

[0002] To evaluate the anti-destroying ability of protective structure, verify the interception efficiency of anti-unmanned aerial vehicle system, when laboratory reproduces real impact scene, unmanned aerial vehicle whole machine is fixed on mobile body, mobile body is driven together by power source, until with 10-100m / s speed impact rigid collision body. Prior art can be divided into two routes according to power source type:

[0003] (1) gas gun-piston scheme-gas gun piston is only out of the barrel when 200m / s or more, unmanned aerial vehicle is light composite material, local stress is extremely high when high-speed push impact, prototype is easily broken by instant, impact state is distorted;

[0004] (2) screw-motor scheme-load is stable, but is limited by critical speed and power, maximum linear velocity is usually lower than 30m / s, cannot meet the demand of high-speed impact test.

[0005] Therefore, prior art is difficult to realize the compatibility of "high speed" and "low impact" simultaneously, a new type of driving scheme is needed, which can accelerate unmanned aerial vehicle to 30m / s or more stably, and avoid local high impact load, so as to solve the feasibility and data effectiveness problem of light unmanned aerial vehicle laboratory impact test. SUMMARY

[0006] The present application is to solve the problems existing in the prior art and provide a kind of simulation unmanned aerial vehicle impact test device.

[0007] The technical scheme adopted by the present application is:

[0008] A kind of simulation unmanned aerial vehicle impact test device, comprising

[0009] Gas driving unit is used to output punch;

[0010] Hydraulic energy storage unit is coupled with the punch, converts punch kinetic energy into controllable hydraulic potential energy and stores temporarily;

[0011] Launch unit includes control valve and launch rod, the control valve is controlled to release the hydraulic potential energy, and launch rod is accelerated;

[0012] Collision body, unmanned aerial vehicle model is driven by the launch rod and moves and impacts collision body to carry out impact test;

[0013] Reset unit is used to reset the launch rod after launch and make hydraulic oil return, realize continuous test.

[0014] Further, the gas driving unit comprises a gas cylinder, a pneumatic cylinder, a punch, a solenoid valve and a diaphragm, the diaphragm is arranged in the pneumatic cylinder and divides the inner cavity of the pneumatic cylinder into a gas storage cavity and a piston cavity, the gas cylinder is communicated with the gas storage cavity through the solenoid valve; after the solenoid valve is opened, the gas storage cavity is pressurized to a set value to break the diaphragm and release the gas which instantaneously enters the piston cavity, so as to push the punch arranged in the piston cavity to accelerate and make the punch obtain kinetic energy.

[0015] Further, the pneumatic cylinder comprises a first cylinder body, a second cylinder body, a flange and a sealing block, the diaphragm is sealingly fixed between two sealing blocks, a flange is fixed on each of the first cylinder body and the second cylinder body, the two sealing blocks are sealingly arranged between the two flanges, and the two flanges are fixed to each other.

[0016] Further, the hydraulic energy storage unit comprises a hydraulic cylinder, a hydraulic piston, a one-way pipeline and an energy accumulator, the hydraulic piston is arranged in the hydraulic cylinder and divides the hydraulic cylinder into a rod cavity and a rodless cavity, one end of the one-way pipeline is connected to the rodless cavity, and the other end of the one-way pipeline is connected to the energy accumulator; the punch hits the hydraulic piston to compress the oil in the rodless cavity, and the oil flows into the energy accumulator through the one-way pipeline.

[0017] Further, the one-way pipeline is sequentially provided with a first one-way valve and a hydraulic lock valve in the liquid flow direction.

[0018] Further, the energy accumulator comprises an energy storage cylinder and a floating piston, the floating piston is arranged in the energy storage cylinder and divides the inner cavity of the energy storage cylinder into a liquid cavity and a gas cavity, and the gas cavity is pre-charged with nitrogen; the oil from the one-way pipeline enters the liquid cavity and pushes the floating piston to compress the nitrogen in the gas cavity, so as to realize potential energy storage; when the floating piston returns, the nitrogen expands to push the oil to be discharged to the launching unit in the reverse direction.

[0019] Further, the launching unit further comprises a launching cylinder, a launching piston and a launching cylinder oil inlet pipeline, the launching piston is arranged in the launching cylinder and divides the launching cylinder into a rodless cavity and a rod cavity, a launching rod is connected to the launching piston, one end of the launching cylinder oil inlet pipeline is connected to the liquid cavity through a control valve, and the other end of the launching cylinder oil inlet pipeline is connected to the rodless cavity of the launching cylinder; the control valve is controlled to be opened, the oil in the liquid cavity instantaneously flows into the rodless cavity of the launching cylinder through the launching cylinder oil inlet pipeline, and the launching piston is pushed to accelerate displacement.

[0020] Further, the reset unit comprises an oil outlet pipeline, a second one-way valve and a reset spring, the reset spring is sleeved on the outer periphery of the launching rod, one end of the reset spring abuts against the end wall of the launching cylinder, and the other end of the reset spring abuts against the launching piston; the oil outlet pipeline connects the rodless cavities of the launching cylinder and the hydraulic cylinder, and the second one-way valve is arranged on the oil outlet pipeline to allow the oil to flow from the launching cylinder to the hydraulic cylinder in one direction.

[0021] Further, the launching rod is arranged on a slide rail, and the launching rod slides on the slide rail under the push.

[0022] Further, the gas driving unit is provided with a pressure gauge, and the hydraulic energy storage unit is provided with an air pressure sensor.

[0023] The present application has the following advantages:

[0024] (1) The present application breaks the limitations of the prior art through the composite driving scheme of "gas driving energy storage + hydraulic potential energy conversion + smooth energy release and emission". Compared with the gas cannon-piston scheme, the device can avoid causing local high stress impact on the lightweight composite unmanned aerial vehicle model and prevent the distortion of the impact state caused by the premature fragmentation of the prototype by means of the potential energy buffer of the hydraulic energy storage unit and the smooth pushing and acceleration of the emission unit. Compared with the screw rod-motor scheme, the device can realize the precise control of the unmanned aerial vehicle model in the speed range of 10-100 m / s by relying on the high initial kinetic energy of the gas driving and the efficient release of the hydraulic potential energy, which can meet the high-speed impact test demand of more than 30 m / s, successfully realize the compatibility of "high speed" and "low impact", and ensure the feasibility of the lightweight unmanned aerial vehicle impact test and the effectiveness of the test data.

[0025] (2) The present application designs the pneumatic cylinder as a split structure combined by a first cylinder body and a second cylinder body, and clamps and fixes the diaphragm through a flange and a sealing block. Compared with the traditional built-in diaphragm structure, the diaphragm can be disassembled and replaced without disassembling the whole cylinder, which greatly simplifies the maintenance process of the vulnerable parts, reduces the long-term operation and maintenance difficulty and cost of the equipment, and ensures the stability and continuity of the power output of the gas driving unit.

[0026] (3) The emission unit of the present application uses a proportional valve as a control valve, which can accurately control the supply rate of hydraulic oil by adjusting the opening degree of the proportional valve, and then flexibly control the acceleration process of the emission rod to realize the precise setting of the final impact speed of the unmanned aerial vehicle model. It can adapt to the impact simulation needs of different types of unmanned aerial vehicles in the range of 15-100 m / s, and can meet the multi-working condition verification of different protection structure anti-destroying ability and different anti-unmanned aerial vehicle system interception efficiency.

[0027] (4) The present application is provided with a reset unit composed of a reset spring, a one-way oil outlet pipeline and a second one-way valve. After a single impact test is completed, the reset spring can automatically push the emission piston and the emission rod back to position, and at the same time drive the hydraulic oil back to the hydraulic cylinder to complete the oil supply, without the need for manual intervention to realize the reset of the device, which provides hardware support for continuous development of multiple repetitive tests and greatly improves the overall efficiency of the test.

[0028] (5) The special collision cabin is arranged for the collision body, the laser speed sensor at the cabin inlet can accurately collect the speed of the unmanned aerial vehicle entering the cabin, and provides a basis for test data calibration; the explosion-proof glass on the cabin side wall can not only block the scattering of impact fragments, ensure the safety of test personnel and surrounding equipment, but also support the high-speed camera equipment to record the whole impact process, so that the key data such as structural response, energy transmission and damage mode can be obtained; meanwhile, the pressure table of the gas driving unit and the air pressure sensor of the hydraulic energy storage unit can monitor the system pressure in real time, and further ensure the controllability and safety of the test process. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 It is a structural diagram of the application.

[0030] Figure 2 It is Figure 1 It is a structural diagram of the collision body.

[0031] Figure 3 It is Figure 2 It is an enlarged schematic diagram of A in the middle (i.e. assembly of the diaphragm).

[0032] Figure 4 It is an assembly diagram of the hydraulic energy storage unit and the reset unit.

[0033] In the figure:

[0034] 1, gas driving unit;

[0035] 10, pressure gauge; 11, gas cylinder; 12, pneumatic cylinder; 121, gas storage cavity; 122, piston cavity; 123, first cylinder body; 124, second cylinder body; 125, sealing block; 13, punch; 14, electromagnetic valve; 15, diaphragm;

[0036] 2, hydraulic energy storage unit;

[0037] 20, air pressure sensor; 21, hydraulic cylinder; 22, hydraulic piston; 23, one-way pipeline; 231, first one-way valve; 232, hydraulic locking valve; 24, energy storage device; 241, energy storage cylinder; 242, floating piston; 243, liquid cavity; 244, gas cavity;

[0038] 3, launching unit;

[0039] 31, launching cylinder; 32, launching piston; 33, launching cylinder oil inlet pipeline; 34, control valve; 35, launching rod;

[0040] 4, collision body;

[0041] 5, reset unit; 51, oil outlet pipeline; 52, second one-way valve; 53, reset spring;

[0042] 6, slide rail;

[0043] The letter A is a magnification icon. DETAILED DESCRIPTION

[0044] The application will be further described below with reference to the accompanying drawings.

[0045] The application is a simulation unmanned aerial vehicle impact test device, comprising a gas driving unit 1, a hydraulic energy storage unit 2, a launching unit 3, a collision body 4 and a reset unit 5, each unit cooperates to realize the smooth acceleration and precise impact of the unmanned aerial vehicle model, and can also complete automatic reset to support continuous test, wherein the gas driving unit 1 is provided with a pressure gauge 10, and the hydraulic energy storage unit 2 is provided with an air pressure sensor 20, which is used for real-time monitoring of the pressure parameter in the system to ensure the stability and controllability of the test process.

[0046] As Figure 1 and Figure 2 , the gas driving unit 1 comprises a gas cylinder 11, a pneumatic cylinder 12, a punch 13, a solenoid valve 14 and a diaphragm 15, the pneumatic cylinder 12 is of split structure and is assembled by a first cylinder body 123, a second cylinder body 124, a flange and a sealing block 125, the diaphragm 15 is sealingly fixed between the two sealing blocks 125, and the two sealing blocks 125 are sealingly arranged between the flanges of the first cylinder body 123 and the second cylinder body 124 respectively, and the diaphragm 15 is stably assembled through the mutual fixation of the flanges. This structure can greatly facilitate the replacement of the diaphragm 15, and only needs to loosen the flange to remove the sealing block 125 to complete the disassembly and assembly of the diaphragm 15.

[0047] In combination Figure 3 , the diaphragm 15 divides the inner cavity of the pneumatic cylinder 12 into a gas storage cavity 121 and a piston cavity 122, the gas cylinder 11 is connected with the gas storage cavity 121 through the solenoid valve 14, and the pressure gauge 10 can monitor the air pressure state in the gas storage cavity 121 in real time. Before the test, the gas storage cavity 121 is inflated through the gas cylinder 11, and when the air pressure in the gas storage cavity 121 rises to a set value, the diaphragm 15 will be broken, the gas will enter the piston cavity 122 instantaneously, and then the punch 13 arranged in the piston cavity 122 will be accelerated to move, so that the punch 13 obtains the initial kinetic energy required for the test.

[0048] The hydraulic energy storage unit 2 comprises a hydraulic cylinder 21, a hydraulic piston 22, a one-way pipeline 23 and an energy accumulator 24, the hydraulic cylinder 21 is fixedly connected with the pneumatic cylinder 12 through the flange, the hydraulic piston 22 is arranged in the hydraulic cylinder 21 and divides the inner cavity of the hydraulic cylinder 21 into a rod cavity and a rodless cavity, one end of the one-way pipeline 23 is connected with the rodless cavity of the hydraulic cylinder 21, the other end is connected with the energy accumulator 24, and a first one-way valve 231 and a hydraulic lock valve 232 are installed in the liquid flow direction of the one-way pipeline 23 in sequence, so as to realize the one-way flow and locking of the oil.

[0049] The energy storage device 24 comprises an energy storage cylinder 241 and a floating piston 242, the floating piston 242 separates the inner cavity of the energy storage cylinder 241 into a liquid cavity 243 and a gas cavity 244, nitrogen is pre-filled in the gas cavity 244, and the gas pressure sensor 20 is connected with the gas cavity 244 to monitor the internal gas pressure in real time.

[0050] When the punch 13 of the gas driving unit 1 obtains kinetic energy, the punch 13 will impact the hydraulic piston 22, the hydraulic piston 22 will compress the oil in the rodless cavity of the hydraulic cylinder 21 after being impacted, the oil flows into the liquid cavity 243 of the energy storage device 24 through the first one-way valve 231 on the one-way pipeline 23, at the same time, the floating piston 242 is pushed to compress the nitrogen in the gas cavity 244, so that the kinetic energy of the punch 13 is converted into hydraulic potential energy and temporarily stored.

[0051] As shown in Figure 4 The launching unit 3 comprises a launching cylinder 31, a launching piston 32 and a launching cylinder oil pipeline 33 in addition to the control valve 34 and the launching rod 35, the hydraulic cylinder 21 is fixedly connected with the launching cylinder 31 through a flange, the launching piston 32 is arranged in the launching cylinder 31 and separates the inner cavity of the launching cylinder 31 into a rodless cavity and a rod cavity, one end of the launching rod 35 is connected with the launching piston 32, and the other end of the launching rod 35 extends to the slide rail 6, and the launching rod 35 is arranged on the slide rail 6 and can stably slide along the slide rail 6.

[0052] One end of the launching cylinder oil pipeline 33 is connected with the liquid cavity 243 of the energy storage device 24 through the control valve 34, and the other end of the launching cylinder oil pipeline 33 is connected with the rodless cavity of the launching cylinder 31, when the hydraulic energy storage unit 2 completes the potential energy storage, the control valve 34 can be controlled to be opened, at this time, the nitrogen in the gas cavity 244 of the energy storage device 24 expands to push the floating piston 242 to move reversely, the oil in the liquid cavity 243 flows into the rodless cavity of the launching cylinder 31 through the launching cylinder oil pipeline 33, and then the launching piston 32 is pushed to accelerate displacement, and the launching piston 32 drives the launching rod 35 to stably slide along the slide rail 6, so that the unmanned aerial vehicle model is stably driven.

[0053] The control valve in the application is a proportional valve, the opening degree and the oil flow ratio of the control valve can be adjusted, the oil supply rate of the hydraulic energy storage unit to the launching unit can be accurately controlled, and then the final impact target speed of the unmanned aerial vehicle model can be flexibly adjusted and controlled.

[0054] The unmanned aerial vehicle model is fixed on the launching rod 35 and moves with the launching rod 35, and moves towards the impact body 4, and finally impacts the impact body 4 to complete the impact test.

[0055] The reset unit 5 comprises an oil outlet pipeline 51, a second one-way valve 52 and a reset spring 53, the reset spring 53 is sleeved on the outer periphery of the launching rod 35, one end of the reset spring 53 abuts against the end wall of the launching cylinder 31, the other end of the reset spring 53 abuts against the launching piston 32, the oil outlet pipeline 51 connects the rodless cavity of the launching cylinder 31 and the rodless cavity of the hydraulic cylinder 21, and the second one-way valve 52 is arranged on the oil outlet pipeline 51, and only allows the oil to flow from the launching cylinder 31 to the hydraulic cylinder 21 in one direction.

[0056] When the impact test is completed, the control valve 34 is closed, at this time, the reset spring 53 pushes the launching piston 32 to retreat, the oil in the rodless cavity of the launching cylinder 31 pushes open the second one-way valve 52, and flows back to the rodless cavity of the hydraulic cylinder 21 through the oil outlet pipeline 51, so that the automatic reset of the launching rod 35 is completed, and the oil for the energy storage link of the next test is supplemented, and the continuous test capability of the device is realized.

[0057] During the whole test process, the pressure gauge 10 can feedback the change of the air pressure in the gas driving unit 1 in real time, so as to facilitate the operator to control the kinetic energy output state of the punch 13, the air pressure sensor 20 can accurately monitor the air pressure in the air cavity 244 of the energy accumulator 24, and the accuracy of the hydraulic potential energy storage is guaranteed, and the design of the split type pneumatic cylinder 12 solves the problem of difficult replacement of the diaphragm 15, so that the whole device can output a speed of 10-100 m / s, meets the impact requirements of the unmanned aerial vehicle, avoids the structural damage of the unmanned aerial vehicle model caused by the local high impact load, and effectively guarantees the effectiveness and accuracy of the impact test data.

[0058] The collision body 4 is a target main body required by the test, which can be replaced by protective components or simulation facilities of different materials and different structures according to actual test requirements, so as to realize the verification of the anti-destroying capability of different protective structures and the interception efficiency of the anti-unmanned aerial vehicle system. The collision body 4 is arranged in a special collision cabin, the launching rod 35 smoothly slides along the slide rail 6 into the collision cabin and collides with the collision body 4. A laser speed sensor is arranged at the entrance of the collision cabin, which can accurately collect the real-time speed of the unmanned aerial vehicle model when entering the cabin, and provide a basis for the effectiveness of the test data; the side wall of the collision cabin is made of explosion-proof glass material, which can effectively block the flying fragments generated after the impact test, avoid damage to the surrounding personnel and equipment, guarantee the safety of the test process, facilitate the intuitive observation of the test personnel, and facilitate the high-speed camera equipment to record the test phenomenon at the moment of impact, so as to obtain key test data such as structural response, energy transmission and damage mode.

[0059] It should be noted that the relative position of the collision body 4 and the collision cabin can be adjusted according to the test working condition, and the fixing structure of the collision body 4 has sufficient rigidity and stability, which can avoid displacement or deformation of the collision body 4 during the impact process, and ensure the accuracy and repeatability of the test data, and adapt to various unmanned aerial vehicle impact simulation test requirements in the speed range of 15-100 m / s.

[0060] The above description is only the preferred embodiment of the present application, it should be pointed out that for those skilled in the art, without departing from the principles of the present application, can also make several improvements, these improvements should also be considered as the protection scope of the present application.

Claims

1. A device for simulating drone impact testing, characterized in that: The utility model relates to a kind of unmanned aerial vehicle impact test device, including Gas drive unit (1), including pneumatic cylinder (12) with punch (13), the pneumatic cylinder (12) includes gas storage cavity (121) and piston cavity (122), punch (13) is located in piston cavity (122), gas storage cavity (121) is stored gas and is boosted to set value after, gas is instantaneously entered piston cavity (122), push the punch (13) for being located in piston cavity (122) acceleration, so that punch obtains kinetic energy; Hydraulic energy storage unit (2), including hydraulic cylinder (21), hydraulic piston (22) and energy accumulator (24), the hydraulic piston (22) is located in hydraulic cylinder (21) and separates hydraulic cylinder into rod cavity and rodless cavity, energy accumulator (24) has liquid cavity (243) and gas cavity (244), liquid cavity (243) and the rodless cavity one-way communication;Punch (13) hits hydraulic piston (22) and makes it compress rodless cavity oil, oil is one-way and gushed into liquid cavity (243) and compresses the gas in gas cavity (244), realizes potential energy storage; Firing unit (3), including control valve (34) and launch rod (35), the control valve is controlled to release the potential energy, and push launch rod acceleration; Collision body (4), unmanned aerial vehicle model is driven after being launched by the launch rod and moves and hits collision body (4) and carries out impact test; Reset unit (5) is used to be positioned after launch and make hydraulic oil return, realize continuous test.

2. The simulated drone impact test device of claim 1, wherein: The gas drive unit (1) further includes gas cylinder (11), electromagnetic valve (14) and diaphragm (15), the diaphragm (15) is located in pneumatic cylinder (12), and the inner cavity of pneumatic cylinder is divided into gas storage cavity (121) and piston cavity (122), gas cylinder (11) is communicated with gas storage cavity (121) through electromagnetic valve (14);After electromagnetic valve (14) is opened, gas storage cavity (121) is boosted to set value and breaks diaphragm (15) and releases gas and is instantaneously entered piston cavity (122), push the punch (13) for being located in piston cavity (122) acceleration, so that punch obtains kinetic energy.

3. The simulated drone impact test apparatus of claim 2, wherein: The pneumatic cylinder (12) includes first cylinder body (123), second cylinder body (124), flange and sealing block (125), the diaphragm (15) is sealed and fixed between two sealing blocks (125), a flange is respectively fixed on the first cylinder body (123) and the second cylinder body (124), two sealing blocks (125) are sealed and placed between two flanges, and two flanges are fixed with each other.

4. The simulated drone impact test apparatus of claim 1, wherein: The hydraulic energy storage unit (2) further includes one-way pipeline (23), one-way pipeline (23) one end is connected with the rodless cavity, and the other end is connected with energy accumulator (24), punch (13) hits hydraulic piston (22) and makes it compress rodless cavity oil, oil is one-way and gushed into energy accumulator (24) through one-way pipeline (23).

5. The simulated drone impact test apparatus of claim 4, wherein: First one-way valve (231) and hydraulic lock valve (232) are sequentially arranged in the liquid flow direction of the one-way pipeline (23).

6. The simulated drone impact test apparatus of claim 4, wherein: The energy storage device (24) comprises an energy storage cylinder (241) and a floating piston (242) arranged in the energy storage cylinder (241) and separating the inner cavity of the energy storage cylinder into a liquid cavity (243) and a gas cavity (244), and nitrogen is pre-charged in the gas cavity (244); oil liquid enters the liquid cavity (243) from the one-way pipeline (23) and pushes the floating piston to compress the nitrogen in the gas cavity, so that potential energy is stored, and the floating piston (242) is pushed by the expanded nitrogen to discharge the oil liquid to the launching unit (3) in reverse when returning.

7. The simulated drone impact test apparatus of claim 6, wherein: The launching unit (3) further comprises a launching cylinder (31), a launching piston (32) and a launching cylinder oil inlet pipeline (33), the launching piston (32) is arranged in the launching cylinder (31) and separates the launching cylinder into a rodless cavity and a rod cavity, the launching rod (35) is connected with the launching piston (32), one end of the launching cylinder oil inlet pipeline (33) is connected with the liquid cavity (243) through the control valve (34), and the other end is connected with the rodless cavity of the launching cylinder (31); the control valve (34) is controlled to be opened, the oil liquid in the liquid cavity (243) is instantaneously poured into the rodless cavity of the launching cylinder through the launching cylinder oil inlet pipeline (33), and the launching piston (32) is pushed to accelerate displacement.

8. The simulated drone impact test apparatus of claim 7, wherein: The reset unit (5) comprises an oil outlet pipeline (51), a second one-way valve (52) and a reset spring (53), the reset spring (53) is sleeved on the outer periphery of the launching rod (35), one end abuts against the end wall of the launching cylinder (31), and the other end abuts against the launching piston (32); the oil outlet pipeline (51) connects the rodless cavity of the launching cylinder (31) with the rodless cavity of the hydraulic cylinder (21), and the second one-way valve (52) is arranged on the oil outlet pipeline (51) to allow the oil liquid to flow from the launching cylinder (31) to the hydraulic cylinder (21) in one direction.

9. The simulated drone impact test apparatus of claim 1, wherein: The launching rod (35) is arranged on a slide rail (6), and the launching rod is pushed to slide on the slide rail (6).

10. The simulated drone impact test device of claim 1, wherein: The gas driving unit (1) is provided with a pressure gauge (10), and the hydraulic energy storage unit (2) is provided with an air pressure sensor (20).

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